Alzheimer's disease (AD) is the most common cause of dementia. There is compelling data that the amyloid- beta (Abeta) peptide plays a key early role in initiating disease pathogenesis. The progressive buildup of toxic forms of Abeta in the brain appears to ultimately lead to downstream events culminating in dementia. Since the concentration of soluble Abeta peptide is directly related to the probability that it will aggregate, determining what normally regulates Abeta levels in the brain will likely provide critical insights ino factors that initiate the AD pathological cascade. The investigators on this PPG proposal have found that synaptic activity is dynamically coupled with the release of the Abeta peptide in the extracellular space of the brain. Our labs have utilized mouse models of AD to discover some of the cellular mechanisms that link synaptic transmission and dynamic changes in Abeta levels in awake, behaving mice with confirmation in human studies. Abeta is dynamically regulated by the sleep-wake cycle and this regulation appears important in determining Abeta deposition later in life. The regulation of Abeta by the sleep-wake cycle may be tied to synaptic activity as brain interstitial fluid (ISF) levels of Abeta are directly coupled with synaptic activity both pre- and post-synapticall. A molecule likely involved in this coupling is LRP1, since APP endocytosis is required for a large component of Abeta generation and LRP1 influences APP endocytosis and Abeta generation. Our hypothesis is that synaptic activity influences both Abeta production and clearance in the brain and that over time this activity influences whether, where, and when Abeta aggregates into toxic species in the brain. In addition, we hypothesize that synaptic activity-mediated Abeta generation and release 1) is influenced by the sleep/wake cycle and molecules that regulate that cycle; 2) occurs in part via post-synaptic stimulation of NMDA receptors via ERK signaling; and 3) is influenced by the LDL-receptor related protein-1 (LRP1) via its interactions with APP. We will combine unique techniques including in vivo protein microdialysis, 13C-labeled amino acid pulse chase labeling combined with mass spectrometry, and focal viral-mediated gene delivery with approaches that assess systems level network function, synaptic and molecular signaling, and cell biology.